One known sheet delivery unit utilizes the overlap method as described in Japanese Patent JP-A-2000-203735 to deliver sheets one by one out of a stack of paper. Another known sheet delivery unit makes use of the retard method described in Japanese Patent JP-A-8-81079 for the same purpose.
In the overlap method, a feed roller rotated at a feeding force to deliver sheets of paper and a gate roller that is brought to a standstill during delivery are made to overlap. A force is produced when sheets of paper are squeezed between the feed and gate rollers and become deformed wavily. Using this force, frictional force is produced between each sheet and the rollers. Thus, the sheets are separated one by one.
The “overlap” means that where the feed roller has two grooves, for example, on its outer surface, with the grooves extending in the direction of rotation, the feed and gate rollers are subtly made to overlap each other such that the outer surface of the gate roller slightly enters the grooves.
In the overlap method of JP-A-8-81079, however, strict accuracy is imposed on the amount of overlap between the rollers. Therefore, accurate rollers are necessitated. For example, where thick sheets of paper are used during a process where paper sheet processing equipment is fabricated, there is the drawback that the amount of overlap needs to be readjusted.
For example, where paper currencies of different thicknesses are treated, separate adjustments are necessary because the thicknesses of paper currencies are different among different nations. To separate the currencies, the amount of overlap must be finely adjusted for each currency thickness.
Furthermore, where a sheet of paper breaks and stays within a sheet delivery unit, if one tries to deliver the sheet, the unit may be clogged up because of increased thickness of the stacked sheets. In this case, automatic delivery cannot be done and the currency fragments must be removed manually.
Furthermore, where a sheet of paper of low rigidity is delivered, it is considered that this sheet is delivered together with following sheets in a stacked form. For example, new paper currencies have higher rigidity and so the amount of overlap is adjusted according to the new currencies. In this case, the ability to separate old currencies, which have been greatly deteriorated due to circulation and have reduced rigidity, (i.e. easily deformed wavily) is reduced greatly.
In the retard method of JP-A-8-81079, a retard roller is made of a softer rubber than the feed roller. During delivery, if a plurality of sheets of paper are fed in, the nip portion (contact portion) of the retard roller is deformed into a concave shape. The front ends of all sheets fed in are brought into direct contact with the retard roller to thereby separate the sheets. That is, the method is intended to concavely deform the nip portion of the retard roller. Therefore, this method is effective for separation of sheets of one kind. However, where sheets of different thicknesses or rigidities are treated, it is impossible to obtain stable separating action over all sheets of paper due to deformation.